WO 2015/158681 A1 discloses a hair cutting appliance, particularly an electrically operable hair cutting appliance, said hair cutting appliance comprising a housing, a cutting head attached to said housing, and a drive train comprising a driving shaft, an output shaft and a coupling linkage, said coupling linkage comprising a driving shaft and a non-aligning output shaft, said coupling linkage comprising a first driving coupling element arranged to be driven by a driving shaft, particularly by a motor shaft, a transmission shaft, particularly a rigid transmission shaft, comprising a first driveable coupling element at a first end and a second driving coupling element at a second end thereof, wherein the first driving coupling element engages the first driveable coupling element for rotatingly driving the transmission shaft, thereby forming a first pivoting joint, wherein the second driving coupling element is arranged to engage a second driveable coupling element of an output shaft, wherein the first driving coupling element and the first driveable coupling element define a male connector comprising an external polygonal profile, viewed in a cross-sectional plane perpendicular to a longitudinal axis, and a female connector comprising an internal polygonal profile, and wherein the external polygonal profile of the male connector, viewed in a longitudinal axial section, is at least sectionally provided with convexly shaped flanks.
In accordance with the arrangement described in WO 2015/158681 A1 a drive train for a hair cutting appliance is provided which is suitable for curved or banana-shaped casings and housings. Consequently, an easy-to-handle appliance may be provided which facilitates operating the appliance which may be beneficial in shaving applications and trimming applications.
In one embodiment, the above WO 2015/158681 A1 relates to a blade set for a cutting head for a hair cutting appliance, wherein the blade set comprises a stationary blade and a moveable blade (cutter) which is arranged to be reciprocatingly moved with respect to the stationary blade. Further, a swiveling mechanism is provided which improves the appliance's ability to follow a skin contour.
Since the blade set including the stationary blade and the cutter is arranged in a pivotable fashion, and since the housing of the appliance is preferably arranged in an elongated but also curved fashion, an angular offset between a motor and an output shaft of the involved drive train is present. For compensating the angular offset, a coupling linkage is presented which comprises at least one transmission joint involving a male part and a female part which are arranged to engage one another, wherein the male part and the female part are provided with polygonal profiles at least one of which is provided with convexly shaped flanks. Consequently, an angular offset between the male part and the female part may be compensated.
The above WO 2015/158681 A1 already provides for a reliable and relatively simple design for an angular offset self-aligning coupling linkage. However, there is still a need for improvement in hair cutting appliances including respective drive trains for angular offset compensation. This may particularly involve user comfort related aspects and performance related aspects. One involved aspect is noise emission. A further involved aspect is vibration emission. Further, it has been observed that, in certain applications, respective driving joints of angular offset compensation drive trains are prone to wear, depending on actual tolerance conditions. If only tight fit or press fit tolerances are present, there is a certain risk of heat generation and related wear. In case too much play is provided and large clearances are present between mating parts, an increase of the noise level may result. This may pose further challenges to the drive train design for hair cutting appliances.